82 
Ionic  Dissociation. 
(Am.  Jour.  Pharm. 
\     February,  1920. 
tend  to  discredit  it,  as  these  are  taken  up  with  more  or  less  detail 
by  most  of  the  textbooks  on  general  chemistry  which  have  been 
published  or  thoroughly  revised  during  the  last  ten  or  fifteen  years. 
As  we  study  chemical  compounds  we  find  that  some,  when  dis- 
solved in  certain  liquids  (water,  in  particular),  conduct  the  electric 
current  in  proportion  to  the  concentration  of  the  solution,  while 
others  do  not.  To  the  class  of  substances  which  conduct  the  current, 
hence  called  "electrolytes,"  belong  the  three  great  classes  of  com- 
pounds— acids,  bases  and  salts. 
According  to  the  Ionic  Theory,  electrolytes,  when  dissolved  in  a 
so-called  "dissociating  solvent,"  decompose  wholly  or  in  part — 
dependent  upon  the  nature  of  the  substance  and  the  concentration 
of  the  solution — into  two  sets  of  particles  or  molecules,  the  members 
of  one  set  being  charged  with  positive  electricity,  the  members  of 
the  other  set  being  negatively  charged,  and  the  number  of  positive 
charges  just  balancing  the  number  of  negative  charges,  the  solu- 
tion being  electrically  neutral.  These  charged  particles  are  called 
"ions"  (meaning  wanderers),  those  of  positive  charge  being  known 
as  "cations,"  those  of  negative  charge,  "anions."  When  an  electric 
current  is  caused  to  pass  through  such  a  solution  the  cations  move 
toward  the  negative  electrode  (the  "cathode")  and  the  anions  move 
toward  the  positive  electrode  (the  "anode")  of  the  decomposing 
cell,  there  losing  their  charges  and  either  separating  as  elements  or 
forming  new  combinations  with  the  water  of  the  solution  or  with 
some  substance  in  the  solution.  Electrolytes  are  frequently  called 
"ionogens." 
Acids  may  be  defined  ionically  as  compounds  which,  when  dis- 
solved in  a  dissociating  solvent,  such  as  water,  yield  hydrogen  ions, 
frequently  called  "hydrions." 
Examples:  HCl  =  H+  +  G1-;  HNO3  -  H+  +  NO3-;  H2SO4  = 
H+  +  H+  -f  SO4-- 
The  hydrions  are  the  cations,  the  CI,  NO3,  SO4,  etc.,  are  the 
anions,  sometimes  called  "acid  ions"  to  correspond  with  the  old 
designation  "acid  radicals,"  as  well  as  to  make  the  matter  more  easily 
understood  by  persons  familiar  with  the  older  theories. 
f  Bases  may  be  defined  ionically  as  compounds  which,  when  dis- 
solved in  a  dissociating  solvent,  yield  hydroxyl  (OH)  ions,  also  known 
as  "hydroxidions." 
Examples:  KOH  =  K+  +  OH";  Ca(0H)2  =  Ca++  +  OR-  + 
OH-;  NH4OH  =  NH4+  +  OH- 
